This invention relates to a substrate which has wiring electrically connected to a semiconductor element and showing excellent characteristics, and in particular to a substrate with wiring which has an excellent anti-hillock characteristic, an excellent anti-pinhole characteristic and a low resistance, and is suitable for use in, for example, an active matrix type liquid crystal display device.
There is an active matrix type liquid crystal display device which has, for example, wiring including a scanning line 1 and a data line 2, etc., a pixel electrode 3, and a thin film transistor 4 as a switching element located in the vicinity of each intersection of the scanning line 1 and the data line 2, as is shown in FIG. 10. The thin film transistor 4 has a gate electrode G connected to the scanning line 1, a drain electrode D connected to the data line 2, and a source electrode S connected to the pixel electrode 3.
FIG. 11 shows a cross section of part of the thin film transistor 4 of FIG. 10. The scanning line 1 including the gate electrode G (see FIG. 10) is formed on a predetermined portion of a glass substrate 11, an anode oxide film 12 is formed on the surface of the scanning line 1, and a gate insulating film 13 is formed on the overall surfaces of the lines and the substrate. A semiconductor thin film 14 made of amorphous silicon is formed on that portion of the gate insulating film 13 which corresponds to the gate electrode G. A blocking layer 15 is formed on a center portion of the semiconductor thin film 14. Ohmic contact layers 16 and 17 made of n.sup.+ -conductivity silicon are formed on upper opposite side portions of the semiconductor thin film 14 and the blocking layer 15. The drain electrode D and the source electrode S are formed on the ohmic contact layers 16 and 17, respectively. These electrodes D and S and the data line 2 may be formed simultaneously. The pixel electrode 3 is formed on a predetermined upper portion of the gate insulating film 13 such that it is connected to the source electrode S. A passivation film 18 is formed on the overall upper surface of the resultant structure, except for on the surface of the predetermined portion of the pixel electrode 3.
It is known that an Al (Aluminum) alloy which contains a high-melting-point metal such as Ti (Titanium) is used as the material of the wiring forming the scanning line 1 with the gate electrode G (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 4-130776). In this case, the high-melting-point metal Ti is contained in Al in order to suppress the occurrence of hillocks, which may well be formed during a heating treatment performed later since Al itself does not have a sufficient thermal resistance. The anti-hillock characteristic is considered to, for example, reduce the breakdown voltage of the gate insulating film 13 on the scanning line 1 including the gate electrode G. If the Ti concentration of the Al--Ti alloy thin film is reduced to lower its specific resistance, occurrence of any hillock and pinhole cannot be suppressed. If, on the other hand, the concentration of Ti is increased, the above drawback can be countered but the specific resistance of the alloy thin film increases. This alloy thin film is not preferable as an electrode or wiring.